(1) The Field of the Invention
This invention relates to novel adhesive compositions and to laminated articles using the novel adhesives presented. More precisely, this invention relates to novel adhesive compositions particularly useful for bonding sheets, film or bodies of polymeric materials to substrate surfaces and to laminates formed by such bonding.
(2) Description of the Prior Art
The bonding of a sheet or film or body of polymeric material to substrate surfaces particularly metal substrate surfaces is well known in the art. Essentially, adhesives used in this application must provide effective bonding between the polymeric material and the substrate surface under the conditions involved in forming the laminate and/or under the conditions of use assigned the laminate. Specialized problems however are presented in preparing laminates formed by bonding sheets of polymeric material and especially thin films of polymeric material to metal surfaces. These problems are particularly apparent in situations where such laminates are later subjected to operations involving shaping or working such as by forming or drawing. Such operations create exceptional stresses between the polymeric material and metal because of the stretching of the bonded materials and special adhesives and bond forming conditions are involved to provide a bond of requisite integrity and endurance during and after the operation.
Bonds of the requisite integrity and endurance have been achieved between polymeric material and metal surfaces using heat curable adhesive systems. Essentially, such bonding involves applying the heat curable adhesive system to at least one of the surfaces to be bonded, heating the applied adhesive to its activation temperature, bringing the other surface in contact with the heat activated adhesive and applying sufficient heat usually together with pressure until bonding (or cure) is complete.
Certain problems, however, have been encountered in the use of known heat curable adhesive systems which are attributed to the relatively high temperatures required to activate the systems. Commercially available heat curable adhesive systems used in laminating thin films of polymeric materials to metal surfaces for example normally require temperatures of above 200.degree. C.--usually 225.degree. C. or higher--for effective activation. High activation temperatures particularly complicate bond forming operations involving thin films of polymeric materials. Avoidance of or compensation for these complications usually requires the use of polymeric materials of specialized heat resistant formulations designed to provide reduced volatility and/or degradation under the bond forming conditions involved and, such formulations are expensive. Relatively expensive plasticizers and/or stabilizers for example are usually involved in such formulations. Moreover, bond forming operations involving thin films of polymeric material having patterned or embossed surfaces, e.g. leather grain or pebble finishes, require special considerations since the bond forming conditions can adversely affect the character of the surface of the polymeric material. High activation temperatures are particularly undesirable in bonding patterned or embossed polymeric materials to metal surfaces. The present invention is addressed to these and other problems presented by the high activation temperatures encountered in heat curable adhesive systems currently employed and presents novel heat curable adhesive systems and novel laminates bonded by the novel adhesive systems.